Frequency Analysis

I'm doing some frequency analysis in SolidWorks. I solved that by using both solvers (FFEPlus, Direct Spares) and using no load as following:

1- In the case of using FFEPlus, the model analysed without any support and constrain. Then 1st eigen frequency was 977.2 Hz.

2- In the case of using Direct Spares, the model analysed with proper support and constrain. Then 1st eigen frequency was 344.96 Hz.

3- In the case of using Direct Spares, the model analysed with activating soft spring option to stabilize the model and no other constrain defined. Then 1st eigen frequency was 978.03Hz.

Now the question is that according to the basic definitions, usually in the case of defining constrains for model we should expect higher eigenfrequency in compare with no-supported model while here I got different results.

Is there any reason to interpret that? And generally which one of mentioned option is more common to do for simple frequency study?